Small radius end mill tool

ABSTRACT

An end mill including a shank having one end gripped by a chuck which is rotatable about a predetermined rotation axis, and a blade body attached to the other end of the shank and rotatable together with the shank. The blade body has a shape in which the area of a cross section in a plane perpendicular to the rotation axis decreases as the distance from the shank increases, and includes a linear cutting edge parallel to, and at a certain distance from, the rotation axis. An end cutting edge adjoining the cutting edge in the longitudinal direction thereof may be provided. The blade body includes, for example, a rake-face-side surface including a rake face and adjoining the flank-side surface in two portions, and a linear cutting edge formed at one of the positions at which the flank-side surface and the rake-face-side surface come in contact with each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/610,611, now U.S. Pat. No. 7,473,059, filed on Dec. 14, 2006, whichclaims priority under 35 U.S.C. §119 to Japanese Patent Application No.2005-360613 filed Dec. 14, 2005, the entire text of which isspecifically incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to an end mill and a method ofmanufacturing the same. More specifically, the present invention relatesto an end mill which is attached to a spindle of a milling apparatus orthe like to be used in the case where a workpiece is machined to form afine groove, and relates to a method of manufacturing the same.

In optoelectronics devices, optical components, such as diffractiongratings and microlens arrays, which have fine structures, are used. Inthis kind of components, forming finer structures is demanded accordingto technical trends such as the reduction of wavelengths of lightsources and the miniaturization of devices. Moreover, thecommercialization of optical integrated circuits in which opticalwaveguides formed on a substrate are combined is in progress.

On the other hand, in medical and biochemical fields and the like,instruments having structures for dealing with very small amounts ofsamples are also used. Such instruments include biochips, microneedlearrays, and chemical micro reactors. In this kind of instruments, too,fine structures are demanded which have higher accuracy and smootherfinished quality.

The entire sizes of products having such a fine structure areapproximately several mm to several tens of mm. On the other hand, forthe form accuracy and the surface roughness of the structure, accuracyof a submicron order to approximately several tens of pm is demanded. Asa method of processing a fine shape on the order of microns, lithographytechnology is known in which semiconductor manufacturing technology isapplied. It should be noted, however, that since molding methods in thiskind of technology utilize chemical reactions, the controllability of aprocessing depth and that of the molding of details such as an edge arelow.

Moreover, in chemical processing methods, the number of steps forcompleting a product is large, and each step takes a certain period oftime. In addition, since a particular chemical reaction is utilized,there are restrictions on a material as an object of processing.Accordingly, it is difficult to mold, for example, lithium niobate whichis a material for an optical waveguide, a germanium lens used in aninfrared optical system, or the like by a chemical processing method.

Other than the above-described chemical processing methods, JapanesePatent Laid-open Official Gazette No. 2002-283174 (Patent Document 1)discloses a high-accuracy machine tool which can perform fine machining.This makes it possible to control the position of a processing tool withaccuracy on the order of microns. Moreover, Japanese Patent Laid-openOfficial Gazette No. 2004-148471 (Patent Document 2) discloses thestructure of an end mill which can be attached to the above-describedmachine tool to perform micromachining. This makes it possible to form afine structure using a tool having a diamond tip. Furthermore, JapanesePatent Laid-open Official Gazette No. 2004-345031 (Patent Document 3)discloses an end mill for micromachining which has other structure. Thismakes it possible to form a fine structure even in a high-hardnessmaterial such as metal.

However, since an object to be machined by the end mill described inPatent Document 2 is a resin material, the bending strength of a cuttingedge portion of the end mill is low. Accordingly, there is a problemthat breakage easily occurs if a metal material which is formed into,for example, a die is machined using this end mill.

Moreover, on the end mill described in Patent Document 3, there is astructural restriction that the crystalline orientation thereof isspecified. For example, in the case where a groove is formed in aworkpiece, it is easy to form a groove having a V-shaped cross sectionin which the opening side is wider, but, on the other hand, it isdifficult to form a machined surface parallel to the rotation axis ofthe end mill.

BRIEF SUMMARY OF THE INVENTION

In order to solve the above-described problems, as a first aspect of thepresent invention, provided is an end mill including: a shank having oneend gripped by a spindle and being rotatable about a predeterminedrotation axis; and a blade body which is bonded to other end of theshank and rotatable together with the shank. The blade body has a shapein which an area of a cross section in a plane perpendicular to therotation axis decreases as distance from the shank increases, and theblade body includes a linear cutting edge parallel to the rotation axisat a certain distance from the rotation axis. Since this end mill hasthe cutting edge parallel to the rotation axis, a rectangular groove canbe machined which has side walls perpendicular to a surface of an objectof machining. Moreover, since the blade body has the area of a crosssection which increases as the distance from the shank decreases,reaction forces from the cutting edge during machining are dispersedover the entire blade body, and the occurrence of stress concentrationin a particular portion can be prevented. Accordingly, high strengthagainst breakage is provided, and high-hardness materials such astooling materials can also be machined.

In the above-described end mill, the blade body may include an endcutting edge adjoining the cutting edge in a longitudinal direction ofthe cutting edge. This makes it possible to efficiently stick the endmill in an object of machining from a surface thereof.

In the above-described end mill, the end cutting edge may be formed at aright angle to the cutting edge, and may be provided to be displacedfrom the rotation axis to one side. This reduces the amount of machiningby each portion of the end cutting edge, and machining is performed bythe highly durable end cutting edge. Accordingly, the bottom surface ofa groove, a hole, or the like formed can be finished to be smooth.

In the above-described end mill, the end cutting edge may be obliquelyprovided to be more protruded as distance from the cutting edgedecreases. This increases the amount of machining by the tip end of theend cutting edge, and high-speed machining can be performed. Moreover,since the cutting edge can be provided to be closer to the rotationaxis, an end mill having a narrower machining width can be formed.

In the above-described end mill, the blade body may include a flank-sidesurface including a flank and having a shape which is part of a curvedsurface of a cone, and a rake-face-side surface including a rake faceand adjoining the flank-side surface in two portions; and the cuttingedge may be formed in one of the two portions in which the flank-sidesurface and the rake-face-side surface come in contact with each other.This makes the blade body supporting the cutting edge have a shape inwhich the cross-sectional shape changes continuously, and reactionforces which the cutting edge is subjected to during machining arethree-dimensionally dispersed over the entire cutting edge. Accordingly,the occurrence of stress concentration in a particular portion of thecutting edge can be prevented.

In the above-described end mill, a central axis of the cone and therotation axis of the shank may intersect each other. This enables thecutting edge formed on the curved surface of the cone to be placedparallel to the rotation axis of the shank.

In the above-described end mill, an extension line of the rotation axisof the shank may pass through a position closer to the flank-sidesurface than the end cutting edge, at the tip end of the blade body.This enables the cutting edge to rotate fast to improve machining speed,and makes the finished quality of a machined surface smooth.

In the above-described end mill, the cone may be a circular cone, andthe rake-face-side surface may be parallel to a central axis of thecircular cone. This makes it possible to easily form the blade body bygrinding.

In the above-described end mill, the rake-face-side surface may be partof any one of a circular conical surface and a cylindrical surface. Thismakes it possible to form the rake-face-side surface with high accuracyusing a rotary grinding tool.

In the above-described end mill, the rake-face-side surface may beformed by grinding a flat surface using a tool having any one of aconical grinding surface and a cylindrical grinding surface. Thisenables the cutting edge to be finished with sharpness.

In the above-described end mill, the other end of the shank may have anend face, which tilts to the rotation axis, and an attachment holeformed perpendicularly to the end face, and the blade body may besupported by one end of a tip, the other end of which is inserted in theattachment hole. This makes it possible to form an end mill in which thetip and a component placed farther from the shank than the tip can bechanged. Accordingly, the end mill can be used economically.

In the above-described end mill, the attachment hole may be a straighthole formed by perpendicularly sticking a tool in the end face afterforming the end face tilting to the rotation axis. This makes itpossible to form the attachment hole with high accuracy. Accordingly,the position accuracy of the tip and the blade body attached thereto isalso improved.

In the above-described end mill, the shank may have a threaded holeformed perpendicularly to the attachment hole from a curved surfacethereof, and the tip may be fixed in place by a screw screwed in thethreaded hole. This facilitates attaching and changing the tip and theblade body.

In the above-described end mill, the tip may have a bonding surfacebonded to an entire bottom surface of the blade body. This enables theblade body to be supported and fixed in place over a wide area.Accordingly, the durability of the end mill is improved.

In the above-described end mill, the tip may have a bonding surfacebonded to the blade body, in which the bonding surface includes abonding surface bonded to part of the rake-face-side surface of theblade body. This enables the blade body to be supported and fixed inplace over a wide area. In addition, the practical bending strength ofthe blade body can be improved by attaching the tip to part of the bladebody.

Moreover, as a second aspect of the present invention, provided is amethod of manufacturing an end mill including a shank and any one of ablade body and a tip attached to one end of the shank in a state inwhich a central axis thereof in a longitudinal direction tilts to arotation axis of the shank. The method includes the steps of: machiningthe one end of the shank to form a tilted end face having a tilt angleto the rotation axis, in which the tilt angle corresponds to an anglecomplementary to the tilt angle of the central axis to the rotationaxis; perpendicularly sticking a tool in the tilted end face to form anattachment hole in which any one of the blade body and the tip isinserted; and fixing in place any one of the tip and an opposite endportion of the blade body from a cutting edge in a state in which anyone of the tip and the opposite end portion of the blade body isinserted in the attachment hole. This prevents a tool for forming theattachment hole from shaking when the tool is stuck. Accordingly, theattachment hole having an appropriate angle to the rotation axis of theshank can be formed with high accuracy. Also, the tip or the blade bodyinserted in the attachment hole enables the cutting edge to be reliablyheld by the shank at an appropriate angle.

The above-described method of manufacturing an end mill may furtherinclude the steps of: forming a threaded hole threaded inside in theshank perpendicularly to the attachment hole; and fixing in place anyone of the blade body and the tip inserted in the attachment hole bypressing any one of the blade body and the tip against an inner surfaceof the attachment hole using a screw screwed in the threaded hole. Thisenables the blade body or the tip to be reliably fixed in place by asimple operation. Also, by loosening the screw, the position of thecutting edge can be readjusted, and a deteriorated cutting edge can beeasily changed.

Furthermore, as a third aspect of the present invention, provided is amilling apparatus including: a spindle head for supporting a rotatablespindle; and an end mill gripped by the spindle and rotatable about apredetermined rotation axis. The end mill includes: a shank having oneend gripped by the spindle; and a blade body having a shape in which anarea of a cross section in a plane perpendicular to the rotation axisdecreases as distance from the shank increases, including a linearcutting edge parallel to the rotation axis at a certain distance fromthe rotation axis, and being bonded to the other end of the shank to berotatable together with the shank. This makes it possible to form a finestructure in a high-hardness material such as a tooling material bymachining using the cutting edge of the end mill having theabove-described features. Accordingly, for example, a die suitable forthe mass production of an optical waveguide, a micro reactor, or thelike can be prepared speedily and easily.

It should be noted that the above-described summary of the inventiondoes not list all features necessary for the present invention and thatsubcombinations of these features can also be included in the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

For more complete understanding of the present invention and theadvantage thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings.

FIG. 1 is a view showing the schematic shape of a milling apparatus 10which is used for machining by attaching an end mill 170 thereto.

FIG. 2 is a perspective view showing a layout in the vicinity of the tipend of the end mill 170 having a blade body 240 attached thereto.

FIG. 3 is a side view of the end mill 170 shown in FIG. 2.

FIG. 4 is a view showing the tip end of the end mill 170 in an enlargedscale.

FIG. 5 is a view showing the tip end of the blade body 240 in anenlarged scale.

FIG. 6 is a view showing the end mill 170 as seen from the direction ofthe tip end of the blade body 240.

FIG. 7 is a view schematically showing a situation in which the bladebody 240 is in contact with a workpiece 30.

FIG. 8 is a view showing the shape of a rectangular groove formed by theend mill 170.

FIG. 9 is a view showing the shape of a blade material 40 in a processfor fabricating the blade body 240.

FIG. 10 is a view showing the shape of the blade material 40 in the nextstep of the process for fabricating the blade body 240.

FIG. 11 is a view showing the shape of the blade material 40 formed intothe blade body 240.

FIG. 12 is a view showing the shape of an end cutting edge flank 246 foran end cutting edge 244 of the blade body 240.

FIG. 13 is a view showing the placement of the end cutting edge 244 inthe blade body 240.

FIG. 14 is a view showing another placement of the end cutting edge 244in the blade body 240.

FIG. 15 is a view showing the blade body 240 having a tip 230 attachedthereto.

FIG. 16 is a view showing the form of an end face 216 of a shank 210 inthe process of manufacture thereof.

FIG. 17 is a view showing the form of an attachment hole 212 in theprocess of manufacture of the shank 210.

FIG. 18 is a view showing the form of a threaded hole 214 in the processof manufacture of the shank 210.

FIG. 19 is a view in which another embodiment of the end mill 170 isshown using the shape of the tip end of a blade body 250.

FIG. 20 is a view schematically showing a situation in which the bladebody 250 is stuck in a workpiece 31.

FIG. 21 is a view showing the shape of a groove formed by the end mill170.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described using embodimentsof the invention. However, the embodiments below are not intended tolimit the invention commensurate with the scope of the claims, and allof a combination of features described in the embodiments are notnecessarily indispensable for solving means of the invention.

FIG. 1 is a perspective view showing the overall shape of a millingapparatus 10 which can be used for micromachining. As shown in FIG. 1,this milling apparatus 10 includes a moving table 120 and a machiningtable 130 which are stacked on a base 110 in order, a supporting post140 which stands upright behind the base 110, and a spindle head 150supported by the front surface of the supporting post 140.

In the upper surface of the base 110, a pair of guide grooves 112 areformed which extend in the back-and-forth direction indicated by arrow Yin FIG. 1. On the lower surface of the moving table 120, protrusions,which cannot be seen in FIG. 1, are formed to fit into the guide grooves112. Accordingly, the moving table 120 can move in the back-and-forthdirection.

In the upper surface of the moving table 120, a pair of guide grooves122 are formed which extend in the width direction of the base 110, thedirection being indicated by arrow X in FIG. 1. On the lower surface ofthe machining table 130, protrusions, which cannot be seen in FIG. 1,are formed to fit into the guide grooves 122. Accordingly, the machiningtable 130 can move in the side-to-side direction.

By combining the movement of the moving table 120 and that of themachining table 130, the machining table 130 can be moved to anarbitrary position within a certain range. It should be noted thatthough not shown, feed screws for controlling the amount of movement of,and for limiting unnecessary movement of, the moving table 120 or themachining table 130 are attached between the base 110 and the movingtable 120 and between the moving table 120 and the machining table 130,respectively. Moreover, in the milling apparatus 10 intended to performaccurate machining, means for biasing the moving table 120 or themachining table 130 in a certain direction is provided in order toeliminate the backlash of each feed screw.

On the other hand, in the front surface of the supporting post 140, apair of guide grooves 142 are also formed which extend in the verticaldirection indicated by arrow Z in FIG. 1. On the back surface of thespindle head 150, protrusions, which cannot be seen in FIG. 1, areformed to fit into the guide grooves 142. Accordingly, the spindle head150 can move along the supporting post 140 in the up-and-down direction.It should be noted that though also not shown, a feed screw forcontrolling the amount of movement of the spindle head 150 and limitingunnecessary movement of the spindle head 150 is attached between thesupporting post 140 and the spindle head 150. In addition, means forbiasing the spindle head 150 in a certain direction is provided in orderto eliminate the backlash of this feed screw.

The spindle head 150 extends forward, and, from the vicinity of thefront end thereof, a spindle provided with a chuck 160 extends downtoward the machining table 130. The chuck 160 is rotationally drivenabout a vertical rotation axis together with the spindle by drivingmeans not shown. The chuck 160 can grip an end mill 170, and the grippedend mill 170 rotates together with the chuck 160.

In the milling apparatus 10, a workpiece 180 as an object of machiningis fixed to the upper surface of the machining table 130 by fixing meansnot shown. The spindle head 150 moves down toward the workpiece 180while rotating the end mill 170 gripped by the chuck 160, and finallysticks the lower end of the end mill 170 in the workpiece 180. Moreover,by moving the machining table 130 or the moving table 120 in this state,a hole or a groove having a desired shape is formed in the upper surfaceof the workpiece 180. Furthermore, by slightly moving the spindle head150 up and down in addition to the movement of the moving table 120 andthe machining table 130, the depth of a groove formed in the workpiece180 can also be changed. It should be noted that these operations canalso be automated by numerically controlling the movement of the movingtable 120 and the machining table 130 and the upward and downwardmovement of the spindle head 150.

FIG. 2 is a perspective view in which the end mill 170 used in a stateof being attached to the milling apparatus 10 is shown alone upside downand in which the vicinity of the tip end (lower end in FIG. 1) of theend mill 170 is schematically shown. As shown in FIG. 2, this end mill170 includes a shank 210 gripped by the chuck 160 of the millingapparatus 10 at the lower end in FIG. 1, a tip 230 attached to an endface 216 of the shank 210, and a blade body 240 bonded to the tip end ofthe tip 230. The end mill 170 further includes a screw 220 for fixingthe tip 230 to the shank 210 by a method such as described later. Itshould be noted that the tip 230 is extended to the inside of the shank210 and that this extended portion is inserted in an attachment hole 212formed in the shank 210.

FIG. 3 is a side view showing the end mill 170 alone as seen from thedirection in which the screw is screwed therein in a state in which theend mill 170 shown in FIG. 1 is turned upside down and in which thecentral axis of the shank 210 is placed upright. As shown in FIG. 3, theblade body 240 is attached to the end face 216 of the shank 210 at aposition displaced from the rotation axis C_(R) of the shank 210 to theright in FIG. 3. Moreover, the blade body 240 has a tapered outsideshape which becomes narrower as the distance from the tip end thereofdecreases. It should be noted, however, that the blade body 240 is seenas a triangle in FIG. 3, which is a side view.

FIG. 4 is a view showing a tip end portion of the end mill 170 which issurrounded by dotted line A in FIG. 3, in a magnified scale. As shown inFIG. 4, in this end mill 170, one edge portion of the blade body 240 isplaced parallel to the rotation axis C_(R) of the shank 210 to form acutting edge 242. Accordingly, the center line C_(C) of the blade body240, which is seen as an isosceles triangle in FIG. 4, tilts at a tiltangle of α to the vertical line V. The center line C_(C) of the bladebody 240 is placed perpendicularly to the end face 216. Accordingly, theend face 216 of the shank 210 tilts at a tilt angle of α to thehorizontal plane H. It should be noted that though the cutting edge 242appears to coincide with the rotation axis C_(R) of the shank 210 inFIG. 4, there is a slight gap therebetween.

FIG. 5 is a view showing the vicinity of the tip end of the blade body240 which is surrounded by dotted line B in FIG. 4, in an enlargedscale. As shown in FIG. 5, the cutting edge 242, which is one edge ofthe blade body 240, is placed parallel to and at a distance of D fromthe rotation axis C_(R) of the shank 210. At the top end of the bladebody 240, a horizontal edge as an end cutting edge 244 is formed toadjoin the cutting edge 242. Accordingly, the center line C_(C) as theoverall shape of the blade body 240 regarded as an isosceles triangleintersects the rotation axis C_(R) of the shank 210 as indicated bydotted lines. When the end mill 170 rotates about the rotation axisC_(R), the cutting edge 242 draws a circle (cylinder) having a radiusequal to the distance D. Accordingly, by pressing the tip end of the endmill 170 against the workpiece in a state in which they are in contactwith each other, the end cutting edge 244 is stuck in the workpiece.

It should be noted that the end cutting edge 244 is provided to bedisplaced from the rotation axis C_(R) to one side (left side in FIG.5), and that the end cutting edge 244 does not exist on the rotationaxis C_(R). Accordingly, the entire end cutting edge 244 is involved inmachining during the rotation of the end mill 170, and therefore theamount of machining by each portion of the end cutting edge 244 becomessmall. Thus, the durability of the end cutting edge 244 is improved, andproperties of a machined surface of the workpiece also become favorable.

FIG. 6 is a view showing the end mill 170 as seen from the direction ofthe tip end of the blade body 240, as indicated by arrow E in FIG. 4. Asshown in FIG. 6, each of portions of the blade body 240 and the tip 230in the vicinities of upper end portions thereof has the same shape as aportion of a circular cone, and is shaped like a half cone having ahorizontal semicircular cross section obtained by cutting the circularcone along the central axis thereof. In the blade body 240, the cuttingedge 242 is formed on a line of intersection between the curved surfaceof the circular cone and the cut surface.

This end mill 170 rotates about the rotation axis C_(R) in the directionindicated by arrow R shown in FIG. 6. Accordingly, for the cutting edge242, the cut surface of the circular cone serves as a rake-face-sidesurface. On the other hand, the surface corresponding to the curvedsurface of the circular cone is a flank-side surface which includes acutting edge flank 241 for the cutting edge 242. Accordingly, when theend mill 170 moves in a lateral direction in a state in which the tipend of the blade body 240 is stuck in the workpiece, the cutting edge242 cuts a portion of the workpiece which is in front of the cuttingedge 242 in the direction of movement.

The use of the above-described end mill 170 makes it possible to machinea fine rectangular groove having a width of approximately several tensof μm with relatively simple equipment. Moreover, since the blade body240 of the end mill 170 has high strength, tooling materials such ascopper and nickel in addition to functional materials such as resin andglass can also be machined. Accordingly, it is also possible tomanufacture an optical waveguide having a fine structure or a die havinga rectangular groove for producing a micro reactor or the like.

FIG. 7 is a view schematically showing a situation in which the bladebody 240 of the end mill 170 is stuck in the workpiece 30. As shown inFIG. 7, in the blade body 240 whose tip end is stuck in the workpiece 30from a machined surface 310 thereof, the end cutting edge 244 forms abottom surface 314 while being stuck in the workpiece 30. Moreover, thecutting edge 242 forms side walls 312. Accordingly, the distance betweenthe pair of side walls 312 formed by this machining becomes twice thedistance D between the rotation axis C_(R) of the end mill 170 and thecutting edge 242. Thus, the end mill 170 forms a groove having the shapeof a doughnut, when it is seen from the upper surface of the workpiece30, and having a flat bottom surface.

FIG. 8 is a view showing the shape of a rectangular groove which can beformed using the end mill 170. As shown in FIG. 7, by moving theworkpiece 30 in a state in which the tip end of the blade body 240 isstuck in the workpiece 30, a rectangular groove having the bottomsurface 314 and the pair of side walls 312 is formed in the workpiece30. At this time, as apparent from the cross-sectional view shown inFIG. 7, the bottom surface 314 of the rectangular groove is parallel tothe machined surface 310. Moreover, each of the side walls 312 of therectangular groove is perpendicular to the machined surface 310.

It should be noted that in the case where a product made using the endmill 170 is a die, a rectangular groove is formed in which the openingside is slightly wider so that a molded product can be removed.Accordingly, in that case, the cutting edge 242 is also formed to beslightly tilted.

FIG. 9 is a view showing one example of an embodiment of a process forfabricating the blade body 240. As shown in FIG. 9, a conical bladematerial 40, which is formed around the central axis C_(C) and which hasa circular bottom surface 248, is used as a material for the blade body240. Such a blade material 40 can be prepared by cutting a round barmade of diamond, boron nitride, aluminum nitride, silicon nitride,alumina, tungsten carbide, or the like to an appropriate length and thenrotationally grinding it. It should be noted that these materials haveextremely high hardness and can therefore be used to machine hardmaterials including metals.

FIG. 10 is a view showing the shape of the blade material 40 in the nextstep of the process for fabricating the blade body 240. As shown in FIG.10, in the blade material 40 which originally has had a conical shape, aflat surface containing the central axis C_(C) is formed so that thebottom surface 248 of the blade material 40 becomes a semicircularshape. This flat surface can be formed by grinding. Thus, a ridge whichultimately serves as the cutting edge 242 is formed at an end portion ofthe curved surface of the conical shape. Moreover, the remaining portionof the curved surface of the conical shape serves as the cutting edgeflank 241 for the cutting edge 242.

It should be noted that though the face serving as a rake face is a flatface parallel to the rotation axis in this embodiment, this face may bea curved surface or a tilted face which becomes closer to the curvedsurface and more distant from the rotation axis as the distance from thebottom surface of the conical shape decreases. For example, in the casewhere the curved surface is formed, a sharper cutting edge 242 can beformed by using a tool having a cylindrical grinding surface andperforming grinding in a state in which the ridge serving as the cuttingedge 242 and the rotation axis of the grinding tool are parallel to eachother. Alternatively, using a grinding tool having a conical grindingsurface, the blade body 240 having the sharp cutting edge 242 and asymmetric shape can be formed by performing grinding in a state in whichthe central axis C_(C) of the blade material 40 and the rotation axis ofthe grinding tool are parallel to each other.

FIG. 11 is a perspective view showing the shape of the blade body 240prepared by further performing the next step on the blade material 40shown in FIG. 10. As shown in FIG. 11, the blade body 240 is the bladematerial 40 shown in FIG. 10 in which the end cutting edge 244 and aflat surface serving as an end cutting edge flank 246 are formed in thetip end thereof. This flat surface serving as the end cutting edge flank246 is formed by grinding the tip end of the blade material 40 using agrinding tool having a flat grinding surface.

FIG. 12 is a side view showing the blade body 240 as seen from thedirection of arrow Q shown in FIG. 11, and particularly showing theplacement of the end cutting edge flank 246 in the blade body 240. Asshown in FIG. 12, the end cutting edge flank 246 is formed to have theend cutting edge 244 as one edge thereof and be tilted at a relief angleof β. This makes it possible to stick the end cutting edge 244 in theworkpiece 30 and machine the workpiece 30.

FIG. 13 is a side view showing the blade body 240 as seen from thedirection of arrow P shown in FIG. 11. It should be noted that in FIG.13, the cutting edge 242 is drawn to be vertical. As shown in FIG. 13,in the blade body 240, the end cutting edge 244 is formed so that theend cutting edge 244 becomes horizontal as indicated by the horizontalline H in FIG. 13 when the cutting edge 242 is placed vertically.Accordingly, the cutting edge 242 and the end cutting edge 244 form aright angle to each other. This makes it possible to machine arectangular groove in which the bottom surface 314 and the side walls312 are perpendicular to each other.

FIG. 14 is a view showing another placement of the end cutting edge 244in the blade body 240. As shown in FIG. 14, in this embodiment, the endcutting edge 244 is at an angle smaller than a right angle to thecutting edge 242, and has an angle of γ to the horizontal line H. Thatis, the end cutting edge 244 is formed to be tilted so that it is moreprotruded in the direction toward the tip end thereof as the distancefrom the cutting edge 242 decreases. This makes the amount of machininglarge at the tip end of the end cutting edge 244, and thereforemachining speed when the end mill 170 is stuck in the workpiece 30becomes high. Moreover, since what is involved in machining is a tip endportion of the end cutting edge 244 in the cutting edge 242 side, anextension line of the rotation axis C_(R) of the end mill 170 can beplaced to pass between one end of the end cutting edge 244 and the otherend thereof. Accordingly, a groove having a narrow width can be machinedby further reducing the distance D between the cutting edge 242 and therotation axis C_(R).

FIG. 15 is a side view showing a composite body 270 formed by bondingthe blade body 240 to the tip 230 in which the blade body 240 is seenfrom the direction of arrow Q in FIG. 11. As shown in FIG. 15, in thevicinity of the tip end of the tip 230, a horizontal bonding surface 231and a vertical bonding surface 233 are formed. The bottom surface 248 ofthe blade body 240 and part of the rake-face-side surface thereof arerespectively bonded to the bonding surfaces 231 and 233 by, for example,brazing. Thus, bonding is performed over wide areas, and sufficientbonding strength is therefore obtained. Moreover, since an extendedportion 232 of the tip 230 which forms the vertical bonding surface 233is attached to the blade body 240 from the side, the bending strength ofthe blade body 240 is supplemented.

In the composite body 270 of the blade body 240 and the tip 230 whichhas the above-described shape and structure, the blade body 240 has sucha shape that the horizontal cross-sectional shape changes continuouslyoverall. Accordingly, reaction forces which the cutting edge 242 and theend cutting edge 244 are subjected to during machining can bethree-dimensionally dispersed overall to prevent the occurrence ofstress concentration in a particular portion. Thus, the practicalbending strength of the blade body 240 becomes high.

FIG. 16 is a side view showing the shape of the shank 210, to which thecomposite body 270 of the blade body 240 and the tip 230 as describedabove is attached, in the vicinity of the end face 216 in the processfor manufacturing the shank 210. As shown in FIG. 16, in the manufactureof the shank 210, the tilted end face 216 having a tilt angle of α isformed at an end portion of a round bar originally having a horizontalend face. It should be noted that in FIG. 16, the orientation of theblade body 240 when the composite body 270 is attached to the shank 210later is indicated by arrow Q shown in FIG. 11 for reference.

FIG. 17 is a view showing a hole-making process performed on the shank210 in the next step of the manufacturing process. As shown in FIG. 17,the attachment hole 212 is formed in an end portion of the shank 210 byperpendicularly sticking a tool in the tilted end face 216. Since theend face 216 is tilted at a tilt angle of α as described previously, theattachment hole 212 is formed to be tilted at an angle complementary tothe tilt angle α to the horizontal plane. It should be noted that inthis hole-making process, a hole-making tool is perpendicularly touchedto and stuck in the end face 216. Accordingly, a machining position anda machining angle do not fluctuate, and the attachment hole 212 isaccurately formed.

FIG. 18 is a view showing a process for making a threaded hole 214 inthe shank 210 in the next step of the manufacturing process. As shown inFIG. 18, the threaded hole 214 has a shape obtained by combining afemale screw 213 threaded and a spot facing 211 to which a head portionof the screw 220 screwed therein is tightly attached. The female screw213 is formed perpendicularly to the attachment hole 212. Accordingly,if the screw 220 is screwed in place in a state in which the compositebody 270 is inserted in the attachment hole 212, the composite body 270is perpendicularly pressed against the inner wall of the attachment hole212, and therefore the attachment position is not displaced in thelongitudinal direction of the composite body 270. Moreover, both theattachment hole 212 and the composite body 270 have circularcross-sectional shapes. Accordingly, even if the diameters of the twodiffer from each other, the attachment angle of the composite body 270is automatically matched to the tilt angle of the attachment hole 212 bythe composite body 270 being pressed against the inner wall of theattachment hole 212. Moreover, the composite body 270 can be easilychanged by loosening the screw 220.

FIG. 19 is a view in which another embodiment of the end mill 170 isshown using the shape of the tip end of a blade body 250 and whichcorresponds to the vicinity of the tip end of the blade body 240surrounded by dotted line B in FIG. 4. As shown in FIG. 19, a linearcutting edge 252, which is one edge of the blade body 250, is placedparallel to and at a distance of D from the rotation axis C_(R) of theshank 210. At the top end of the blade body 250, a quadrant-shaped endcutting edge 254 is formed whose one end adjoins the cutting edge 252.Here, the other end of the end cutting edge 254 extends to theintersection with the rotation axis C_(R). At this endpoint, the tangentto the end cutting edge 254 becomes horizontal.

When the end mill 170 provided with the blade body 250 as describedabove rotates about the rotation axis C_(R), the cutting edge 252 drawsa circle (cylinder) having a radius equal to the distance D. Moreover,by pressing the tip end of the end mill 170 against a workpiece in astate in which they are in contact with each other, the end cutting edge254 is stuck in the workpiece. Moreover, since the arc-shaped endcutting edge 254 rotates to form a hole or a groove in the workpiece,the bottom surface of the hole or the groove has a semicircularcross-sectional shape. The end cutting edge 254 having such a shape canbe made by grinding the tip end of the blade material 40 shown in FIG.10 using a rotary grinding tool whose inner surface has a semispheregrinding surface and which rotates about the center of the grindingsurface, a disk-shaped rotary tool in which the peripheral surfacethereof has a groove having a semicircular cross section, or the like.

FIG. 20 is a view schematically showing a situation in which the bladebody 250 of the end mill 170 is stuck in a workpiece 31. As shown inFIG. 20, in the blade body 250 of which tip end is stuck in theworkpiece 31 from a machined surface 310 thereof, the end cutting edge254 forms a bottom surface 314 having a semicircular cross-sectionalshape while sticking in the workpiece 31. The cutting edge 252 formsside walls 312 perpendicular to the machined surface of the workpiece31. It should be noted that though the tip end of the end cutting edge254 ends at the rotation axis C_(R) because FIG. 20 is a schematic view,the end cutting edge 254 is preferably extended beyond the rotation axisC_(R) in order to smooth the bottom surface of the groove. In that case,the shape of the end cutting edge 254 is an arc larger than a quarter ofa circle.

FIG. 21 is a view showing the shape of a groove formed by the end mill170 having the blade body 250 shown in FIG. 19. When the workpiece 31 ismoved in a state in which the tip end of the blade body 250 is stuck inthe workpiece 31 as shown in FIG. 20, a groove having the bottom surface314 and the pair of side walls 312 is formed in the workpiece 31. Atthis time, as apparent from the cross-sectional view shown in FIG. 20,the bottom surface 314 of the groove has a semicircular cross-sectionalshape. In addition, each of the side walls 312 of the groove isperpendicular to the machined surface 310.

It should be noted that in the case where a product made using this endmill 170 is a die, a groove is formed in which the opening side isslightly wider so that a formed product can be removed. Accordingly, inthat case, the cutting edge 252 is also formed to be slightly tilted.

As described above, according to this embodiment, since the cutting edge242 or 254 parallel to the rotation axis is provided, a rectangulargroove can be machined which has side walls perpendicular to the surfaceof an object of machining. Moreover, the blade body 240 or 250 has across-sectional area which becomes larger as the distance from the shank210 decreases and the change of the cross-sectional area is continuous.Accordingly, reaction forces from the cutting edge 242 during machiningare dispersed over the entire blade body 240 or 250, and stressconcentration does not occur in a particular portion. Thus, highstrength against breakage is provided, and high-hardness materials suchas tooling materials can also be machined.

Although the present invention has been described above usingembodiments, the technical scope of the present invention is not limitedto the scope of the description of the embodiment. It is apparent tothose skilled in the art that various modifications and improvements canbe made to the above-described embodiments. It is apparent from thedescription of the scope of claims that embodiments in which suchmodifications and improvements are made can also be included in thetechnical scope of the present invention.

Although the preferred embodiments of the present invention have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made therein without departing fromspirit and scope of the inventions as defined by the appended claims.

1. An end mill comprising: a shank having one end gripped by a spindle,the shank being rotatable about a predetermined rotation axis; and ablade body held at the other end of the shank, the blade body beingrotatable together with the shank, wherein the blade body has a shape inwhich an area of a cross section in a plane perpendicular to therotation axis decreases as distance from the shank increases, and theblade body includes a linear cutting edge parallel to the rotation axisat a certain distance from the rotation axis, wherein the blade bodyincludes a conical surface portion and a flat surface portion thatintersect to form the linear cutting edge, and wherein an angle of theblade body with respect to the shank is nonvariable.
 2. The end millaccording to claim 1, wherein the blade body includes an end cuttingedge adjoining the linear cutting edge.
 3. The end mill according toclaim 2, wherein the end cutting edge is formed at a right angle to thelinear cutting edge, and is disposed to be displaced from the rotationaxis to one side.
 4. The end mill according to claim 2, wherein the endcutting edge is obliquely disposed relative to the linear cutting edge.5. The end mill according to claim 1, wherein the conical surfaceportion is a flank-side surface of the blade body, and wherein the flatsurface portion is a rake-face-side surface adjoining the flank-sidesurface in two portions, and wherein the linear cutting edge is formedin one of the two portions in which the flank-side surface and therake-face-side surface come in contact with each other.
 6. The end millaccording to claim 5, wherein a central axis of the cone and therotation axis of the shank intersect each other.
 7. The end millaccording to claim 5, wherein the cone is a circular cone, and therake-face-side surface is parallel to a central axis of the circularcone.
 8. The end mill according to claim 5, wherein the rake-face-sidesurface adjoins an end cutting edge of the blade body.
 9. The end millaccording to claim 5, wherein the rake-face-side surface is formed bygrinding a flat surface using a tool having any one of a conicalgrinding surface and a cylindrical grinding surface.
 10. The end millaccording to claim 1, wherein the other end of the shank has an end facetilting to the rotation axis and an attachment hole formedperpendicularly to the end face, and the blade body is supported by oneend of a tip, the other end of the tip being inserted in the attachmenthole.
 11. The end mill according to claim 10, wherein the attachmenthole is a straight hole formed by perpendicularly sticking a tool in theend face after forming the end face tilting to the rotation axis. 12.The end mill according to claim 11, wherein: the shank has a threadedhole formed perpendicularly to the attachment hole from a surfacethereof, and the tip is fixed in place by a screw screwed in thethreaded hole.
 13. The end mill according to claim 10, wherein the tiphas a bonding surface bonded to an entire bottom surface of the bladebody.
 14. The end mill according to claim 10, wherein the tip has abonding surface bonded to the blade body, the bonding surface includinga bonding surface bonded to part of a rake-face-side surface of theblade body.
 15. A milling apparatus comprising: a spindle head forsupporting a rotatable spindle; and an end mill gripped by the spindleand rotatable about a predetermined rotation axis, wherein the end millcomprises: a shank having one end gripped by the spindle; and a bladebody having a shape in which an area of a cross section in a planeperpendicular to the rotation axis decreases as distance from the shankincreases, including a linear cutting edge parallel to the rotation axisat a certain distance from the rotation axis, and being held at theother end of the shank to be rotatable together with the shank, whereinthe blade body includes a conical surface portion and a flat surfaceportion that intersect to form the linear cutting edge, and wherein anangle of the blade body with respect to the shank is nonvariable.